1. Field of the Invention
The invention relates, in general, to wireless systems and more particularly to channel switching for interoperable safety and non-safety communications in wireless environments.
2. Discussion of the Related Art
The 5.9 GHz DSRC (“Dedicated Short Range Communications”) spectrum allocation is shown in FIG. 1. Channels 172, 174, 176, 178, 180, 182, and 184 are shown in FIG. 1. Notably, a control channel is found on channel 178, service channels are found on channels 174 and 176, and safety channels are found on channel 172 and 184. FCC Memorandum Opinion and Order FCC-06-110 contains further information about the spectrum allocation.
Notably, FCC-06-110 mandates that channel 172 is designated for public safety applications involving safety of life and property.
FCC-060-110 also mandates that channel 184 is designated for public safety applications involving safety of life and property. Only those entities meeting the requirements of FCC 90.373(a) are eligible to hold an authorization to operate on this channel.
IEEE 802.11p is an approved amendment to the IEEE 802.11 standard to add wireless access in vehicular environments (WAVE). It defines enhancements to 802.11 required to support Intelligent Transportation Systems (ITS) applications. This includes data exchange between high-speed vehicles and between the vehicles and the roadside infrastructure in the licensed ITS band of 5.9 GHz (5.85-5.925 GHz). IEEE 1609 is a higher layer standard on which IEEE 802.11p is based.
A proposed requirement for WAVE multi-channel interoperability is explained below. WAVE multi-channel operations shall be scheduled in a way that ensures interoperable communications among a mixture of various WAVE devices for both safety and non-safety applications conducted on the safety channels and the non-safety channels, respectively.
Typical WAVE device types operating on the safety channels is described below with reference to FIGS. 2 and 3. In FIG. 2, the operation of single-PHY (physical layer) devices is shown. A first type of single-PHY device operation is shown in FIG. 2A. Type A devices are CCH-SCH-Switching devices (control channel, service channel). In FIG. 2A the control channel CCH is interleaved with service channels SCH1 and SCH2. A second type of single-PHY device operation is shown in FIG. 2B. Type B devices are Safety-Channel-only devices. Note that the device is only tuned to safety channel SafetyCH1. In FIG. 3, the operation of dual or multi-PHY (physical layer) devices is shown. Type D devices have, for example, two radios that are both channel switching capable. Radio 1 switches between control channels and safety channels, whereas radio 2 is tuned to the safety channel.
The interoperability of various single-PHY WAVE devices on the safety channel is shown below with reference to FIGS. 4-6.
Case 1 is shown in FIG. 4 wherein Device 1 and Device 2 are both type A devices. There is no problem with this case, as the type A devices are compatible having similar switching between the safety and control channels as shown.
Case 2 is shown in FIG. 5 wherein Device 1 and Device 2 are both type B devices. There is no problem with this case either, as the type B devices are both tuned to the safety channel, SafetyCH1.
Case 3 shows a mixture of type A and B devices, which is problematic. This is obviously due to the fact that the type A device switches between the control and service channels, whereas the type B device is tuned to the safety channel SafetyCH1.
The operation of typical WAVE device types on the non-safety channels is shown below with reference to FIG. 7. WAVE devices only for non-safety services (e.g. tolling), are herein called type “T” devices. A type T (one-radio) Road-side Unit (RSU) switches synchronously to the CCH in order to transmit its WSA, and then after transmission switches asynchronously to the SCH to perform a service. The worst case is an asynchronous type T On-board Unit (OBU). The OBU is normally sleeping, and upon activation, tunes to the CCH, with no GPS. Upon receiving the WSA, switches to the SCH for conducting services. The OBU goes back to sleep after services are completed.
Hence, there remains a need for improved interoperability for safety and non-safety communications in wireless environments.